static public long Choose(int n, int k, bool isSorted, bool isUnique)
{
long result = 1;
if (!isSorted && !isUnique)
{
for (int i = 0; i < k; i++)
{
result *= n;
}
}
if (!isSorted && isUnique)
{
result = Combinatorial.C(n, k) * Combinatorial.Factorial(k);
}
if (isSorted && isUnique)
{
result = Combinatorial.C(n, k);
}
if (isSorted && !isUnique)
{
result = Combinatorial.C(n + k - 1, k);
}
return(result);
}
public long count(string n)
{
long result = 0;
int[] digits = new int[10];
for (int i = 0; i < n.Length; i++)
{
digits[n[i] - '0']++;
}
while (n != "")
{
for (int i = 0; i < n[0] - '0'; i++)
{
if (digits[i] > 0)
{
int k = n.Length - 1;
long x = 1;
digits[i]--;
for (int j = 0; j < 10; j++)
{
x *= Combinatorial.C(k, digits[j]);
k -= digits[j];
}
digits[i]++;
result += x;
}
}
digits[n[0] - '0']--;
n = n.Substring(1);
}
return(result);
}
